The object of this work is to provide a molecular framework with which to characterize B and T lymphocyte differentiation and function. This framework takes the form of recombinant DNA clones of B or T cell specific genes isolated through messenger RNA subtraction procedures (cDNA absorption, selected cDNA cloning) developed in this laboratory. During this past year we have concentrated our efforts in several regards: 1) estimating the differences in gene expression between B or T lymphomas and between tumors within the B or T lineage; 2) establishing libraries of B and T cell specific genes from selected tumors (selected cDNa libraries); 3) screening selected libraries for genes coding for cell surface and secreted proteins; 4) screening selected libraries for gene mapping to the X chromosome. In particular, we have isolated and partially characterized an X-linked gene family (TX-1) expressing multiple messenger RNA's in T helper hybridomas but not in other types of B and T cell tumors and hybridomas.